This invention relates to air-fuel ratio regulating apparatus for regulating the ratio of air to fuel of a fuel-air mixture supplied to internal combustion engines, and more particularly to an air-fuel ratio regulating apparatus which is adapted to automatically regulate the air-fuel ratio of a fuel-air mixture supplied to an internal combustion engine for a motor vehicle or the like in order to reduce the amounts of toxic components of exhaust gases.
The systems which have hitherto been proposed as means for effecting control of exhaust emissions of motor vehicle engines can be broadly classified into the following three types: a first type which uses means for effecting control in the suction system, a second type which uses means for effecting control in the exhaust system and a third type which relies on providing improvements in the combustion of a fuel-air mixture itself. Meanwhile the amounts of hydrocarbons, carbon monoxide and oxides of nitrogen in exhaust gases depend to a large extent on the air-fuel ratio of a fuel-air mixture supplied to the combustion chamber. If it is possible to automatically and positively regulate the air-fuel ratio, the accuracy with which the aforesaid exhaust emission control means are required to perform will be greatly lowered and the exhaust emission control means can be done without in some cases. In the prior art, the system from the supply of fuel to the engine to venting of exhausts therefrom constitutes an open loop. Thus, the prior art systems of exhaust emission control have the disadvantage of being unable to achieve excellent results as expected in terms of the cost of production, unless the accuracy of performance of each device is increased as much as possible.
Thus, it can be foreseen that, if it is possible to automatically regulate the air-fuel ratio of fuel-air mixtures supplied to the combustion chamber based on the value of one component of exhaust gases which is detected, the burden borne by each exhaust emission control means will decrease and the end of cleaning the exhaust gases can be attained at low cost.
With this point in view, proposals have hitherto been made to use a fuel supply device relying on the feedback system. The present state of art is such, however, that these proposals involve the use of complex circuitry and no satisfactory results can be achieved in spite of the use of such circuitry.
Of the proposals made so far, a proposal which has the highest possibility of being able to be put to practical use concerns a method wherein the oxygen in exhaust gases is detected by an oxygen detector element (O.sub.2 sensor) and the air-fuel ratio of an fuel-air mixture supplied by the carburetor is regulated by the output of this element to be approximate to the theoretical air-fuel ratio, so that the oxidizing catalyst device mounted in the exhaust system can operate with a highest conversion rate and exhaust emissions can be controlled satisfactorily to avoid the problem of air polution. Some disadvantages are associated with this method. The control circuit used for this method is complex in construction, and the control of the air-fuel ratio may go away due to a disturbance because such control is basically a proportional control. Particularly, the fundamental drawback is that there is a variation in the results obtained by regulating the air-fuel ratio owing to variations in the characteristics of O.sub.2 sensors caused by changes with time or variations in characteristics from one O.sub.2 sensor to another. Thus, it is necessary to increase the accuracy with which other exhaust emission control devices are required to perform by taking variations in the characteristics of the O.sub.2 sensors and their deterioration into consideration. This results in a marked reduction in the durability and reliability of these exhaust emission control devices, thereby causing an increase in cost which might otherwise be avoided.